Axial piston pumps and motors with rotary cylinder blocks



Nov. 12, 1963 K. VETTER ,110, 7

AXIAL PISTON PUMPS AND MOTORS WITH ROTARY CYLINDER BLOCKS Filed June 24, 1959 INVENI'OP Karl I/eHer BY 7 42 Sirllfer ATTORNEY United States Patent Ofi ice 3,llfl,2ti7 Patented Nov. 12, 1963 3,110,267 AXIAL PISTGN PUMPS AND MOTGRS WETH RGTARY CYLHNDER BLGCKS Kari Wetter, Heiligenhaus, Germany, assignmto Gesellsehaft fuer Lindes Eismaschinen Ahtiengeseilsehaft Zweigniederiassnng Gueldner-Motoren-Werke, Aschaffenburg, Aschaffenhurg, Germany Filed June 24, 1959, er. No. 822,597 Qlaims priority, application Germany June 36,- 1958 12 Slaims. (Cl. 163-162) The present invention relates to piston pumps and motors in general, and more particularly to an axial piston pump or motor having a rotary cylinder block.

it is already known to utilize in axial piston pumps and motors a cylinder block which is formed with a central bore for the passage of a bolt, pin or stud fixed to a stationary element of the pump with whose control surface an end face of the rotary cylinder block cooperates. The central bore is formed with an enlarged zone or recess which constitutes a single pressure chamber, the latter communicating with the high-pressure side of the pump or motor and being sealed at one of its sides by a bushing or sleeve which surrounds the aforementioned bolt. The bushing which is axially slidable with respect to the cylinder block and is fixed for rotation to the bolt is formed with a flange which extends beyond the cylinder block. The pump or motor further comprises a resilient element which is installed between the bushing and a stop or abutment on the aforementioned bolt, the purpose of the stop being to take up the forces acting between the block and the stationary part. ternately, the bushing may be replaced by a shouldered boss forming part of the bolt which is then axially slidable in the suitable shaped central bore of the stationary element of the pump or motor with respect to the cylinder block and is constantly biased by a spring inserted between a stop on the bolt and the aforementioned stationary element whose control surface cooperates with an end face of the rotary cylinder block. When no pressure exists in the pressure chamber formed by the recess in the shaped axial bore of the cylinder block, the latter is urged by the spring means over the bushing, or directly by the bolt, to move its end face into requisite position with respect to the control surface of the stationary element. When the pressure in the chamber rises, the fluid urges the end face of the cylinder block into abutment with the control surface and simultaneously overcomes the force of the spring means whereby the bushing or the bolt is axially displaced with respect to the cylinder block. During such movement, a flange on the bushing or on the bolt is displaced in a direction away from the cylinder block, thus terminating the friction between the flange and the block, the latter being thereupon held in proper relationship with respect to the control surface solely by the pressure of hydraulic fluid in the aforementioned chamber. Communication between the pressure chamber and the high pressure side of the pump or motor assembly is established over suitable check or non-return valves independently of which side of the as sembly is the high-pressure side, this depending upon the momentary direction in which the cylinder block rotates and also upon the direction of fluid delivery.

An important object of the present invention is to provide a pump or motor assembly of the above outlined characteristics which can operate without check valves.

Another object of the invention is to provide an axial piston pump or motor assembly in which the rotary cylinder block is constantly and securely retained solely by hydraulic pressure against movements with respect to the control surface on a stationary element of the apparatus.

A further object of the invention is to provide a pump or motor assembly in which the sealing engagement between the rotary cylinder block and the control surface of an adjacent stationary part can be maintained independently of the changes and fluctuations in pressures prevailing at the highor low-pressure side of the apparatus.

An additional object of the instant invention is to provide an improved axial piston pump or motor assembly which is particularly useful when it forms part of a serially connected train of pumps or motor assemblies.

Still another object of the invention is to provide an axial piston pump or motor assembly utilizing a rotary cylinder block which is so constructed that the tilting forces acting upon the cylinder block are reduced or completely eliminated.

A concomitant object of the present invention is to provide a pump or motor assembly of the above outlined characteristics in which the pressure losses due to leakage of fluid pressure medium are reduced to a minimum.

With the above objects in View, the invention resides essentially in the provision of an axial piston pump or motor assembly having a rotary cylinder block formed with a shaped central bore receiving a suitably shaped pin or bolt, or a bolt combined with a shaped sleeve or bushing, defining with the cylinder block two spaced pressure chambers in said bore. Both pressure chambers are bounded at their opposing sides by two equally dimensioned shoulders of the bolt or of the bushing on the one hand, and by two spaced shoulders of the cylinder block on the other hand, and are connected, respectively, to the highand low-pressure sides of the apparatus. Such arrangement renders it possible to dispense with the aforementioned check valves since, depending upon the direction of fluid delivery and upon the direction in which the cylinder block rotates, the one, the other, or both pressure chambers are always connected with the high-pressure side of the system and thus insure that an end face of the cylinder block remains in proper position with respect to the control surface on -a stationary part of the apparatus, i.e. an axial piston pump or motor assembly.

Another important advantage of such construction is in that the cylinder block is always held against the control surface by hydraulic pressure conveyed to its annular shoulders through one or both chambers from the momentary high-pressure side of the apparatus. As is known, the control surface and the end face of the rotary cylinder block define therebetween a control gap which com-municates with substantially kidney-shaped arcuate recesses in the control surface. The pressure or" fluid medium prevailing in uch kidney-shaped recesses tends to move the cylinder block away from the control surface, and the advantage of the aforementioned twin pressure chambers is that at least one thereof always communicates with the recess in which a higher pressure prevails and the pressure of fluid medium therein effectively counteracts the pressure of fluid in the one or the other kidney-shaped recess.

Thus, the operation of the novel pumping or motor assembly is completely independent of the pressures prevailing in the one or the other recess at the momentary highor low pressure side of the apparatus. This is particularly important when the pressure fluid is delivered to the pump or motor at different pressures, or when a number of such pumps or motors is connected and operated in series. By the provision of two pressure chambers, the tilting forces acting upon the cylinder block may remain comparatively small or are eliminated altogether even if the pressures at the highor low-pressure side should vary within wide limits. Such tilting forces arise because of different median distances at which the pressure of the fluid medium acts in the individual cylinder spaces of the cylinder block and against the end face of the latter, especially when the aforementioned kidney-shaped recesses and the passages leading therefrom to the indi idual cylinder spaces are of rather small diameters and are concentrated in a small zone. By concentrating the recesses and the passages in a comparatively small zone, the sealing surface between the recesses and the outer diameter of the control surface on the stationary part of the apparatus may be very wide which, in turn, reduces losses due to leakage between the end face of the cylinder block and the control surface.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following detailed description of two specific embodiments when read in connection with the accompanying drawing, in which:

FIG. 1 is axial section through an axial piston pump assembly having two pressure chambers formed in the central bore of its rotary cylinder block, in wluch one side of each pressure chamber is sealed by equal surfaces on two shoulders of a bushing non-rotatably mounted on the bolt; and

FIG. 2 is a similar axial section through a slightly modified pump assembly in which the bushing is replaced by a boss forming an integal part of the bolt or pin which connects the cylinder block to the stationary element or part with whose control surface the end face of the block is adapted to cooper-ate.

Referring now in greater detail to the illustrated embodiments, and first to that shown in PEG. 1, the pump assembly P comprises 'a cylinder block 1 which is rotated by a piston element or wobble plate 2 through a plurality of rods 3 and plungers 4. There is a swivel or universal connection 3a between one end of each rod 3 and the piston element 2', and a similar universal articulate connection 3b between the other end of each rod 3 and the respective plunger 4-. By inclining the axis of piston element 2 with respect to the of cylinder block 1, the plungers 4 perform alternating suction and compression or delivery strokes in their respective cylinder spaces 5. The flow of fiuid medium is controlled by the surface 6 of a stationary element or part 6 which is in virtual abutment with the adjacent end face 7 of the cylinder block 1, a thin gap or slit filled with a lubricant being formed between the surfaces 6 and 7. The stationary part 6 is formed with customary substantially kidney-shaped recesses or openings 6a, 6b communicating with channels 10, 11 which latter, depending upon the direction in which the cylinder block 1 rotates, and also depending upon the momentary angular position of the piston element 2 with respect to the axis of cylinder block 1, alternately ccnstitute the high and low-pressure sides of the pump assembly P.

It is often desirable to supply pressure fluid to the apparatus P at a certain initial pressure whereby the highand the low-pressure sides of the pump are under higherthan-atmospheiic pressure. The difference between normal and super-atmospheric initial pressures of the fluid may be of varying magnitudes.

The pressure prevailing in the gap between the surfaces 6 land 7, and the pressure of fluid in the recesses 6a, 6b formed in the surface 6, tend to move the cylinder block 1 away from the control surface 6. This is prevented by the provision of a bolt or pin 8 which is integral with the stationary part 6' and extends into and beyond the shaped central axial bore 10 formed in the cylinder block 1. This bore comprises two concentric axially spaced annular enlarged zones 9, 9 which constitute two pressure chambers and communicate with channels l0, 11 through passages 12, 13, respectively, formed in the pin or bolt 8 and in the stationary part 6. Thus, the pressure of fluid prevailing in recesses 60, 6b is conveyed through channels 10, 12 and 11, 13 to the fluid filling the chambers 9, 9, respectively, and the fluid in these chambers transmits the pressure to the equal-area surfaces on shoulders l9, 19 formed in the bore 1:: of cylinder block 1. Shoulders 1%, 19 are turned away from the end face 7. The pressures prevailing in the cylinder spaces 5 act in the same direction as, and thus assist the pressure of, the fluid filling cham hers 9, 9 in holding the end face 7 in proper position with respect to the control surface 6. Cylinder spaces 5 communicate with the recesses 6a, 612 through bores 50 formed in the cylinder block 1. The pressure of fluid in cylinder spaces 5, in channels or bores 5a! and in chambers 9, 9' opposes the fluid pressure in the very small gap between the surfaces 6, 7 and in the recesses 6a, 6b which latter pressure tends to move the cylinder block 1 away from the stationary part 6. By suitable dimensioning of the surfaces exposed to the pressure of fluid medium, the resultant force of all oppositely directed forces may be so adjusted that no tilting of the cylinder block 1 can take place.

In addition to the annular surfaces of aforementioned shoulders 19, d9, the pressure chambers 9, 9 are bounded by the surfaces of two annular shoulders 14, 14, respectively, of equal area and formed by a suitably shaped bushing 15 mounted on the bolt 8. The construction of the pump assembly P shown in FIG. 2 diifers from that illustrated in FIG. 1 in that the bushing 15 is replaced by a suitably shaped bolt 1G8 which is integrally formed with a stepped boss having shoulders 114, 114- corresponding to the shoulders 1-4, 14, respectively. Whle the bolt 8 of FIG. 1 is integrally formed with the stationary part 6, it obviously cannot rotate with respect to the latter but is axially slidable with respect to the cylinder block 1 and with respect to the bushing 15 which latter is non-rotatably fixed thereto by a key 15a. The extent to which the bolt 8 may move axially with respect to the cylinder block 1 and sleeve or bushing 115 under the influence of fluid pressure prevailing in chambers 9, 9 is controlled by resilient means here shown as a plate spring 17 which is inserted between a flange 16 of the bushing '15 and a stop 18 fixed to the free end of bolt 8. The stop 18 may assume the shape of a preferably non-circular nut which is screwed onto the externally threaded end of the bolt 8.

In FIG. 2, the bolt or pin 168 is axially movable with respect to the stationary part 166 under the influence of fluid pressure prevailing in pressure chambers 169, 199'. The axial movements relative to the part 106' are limited and controlled by a plate spring 117 which acts between the outer side 166s of part 106 and a stop here shown as a nut 118 which is screwed onto the externally threaded free end of bolt 108. The communication between the chambers 1. .69, 109 and substantially kidney-shaped recesses 1060!, 1815b in the control surface 105 is established through channels or passages 5.12, 1-13 in bolt 108, by an annular recess 120 in the bore 1%.! of stationary part 106, and by radial passages 121, 122 connecting the recess 129 with the channels 191i 111, respectively, which latter convey fluid to the kidneyshaped recesses 105a, 1436b. The flange 1 16 at the lefthand end of the boss forming part of the bolt Ill-8 is adjacent to the left-hand end face of the cylinder block 1. The construction and mounting of parts 1, 2, 3 and 4 are identical with that of corresponding parts shown and described in connection with FIG. 1.

When a certain pressure prev-ails in chambers 9, 9 or 109, 199, the bushing 15 (FIG. 1) or the bolt 198 (FIG. 2) assumes the position shown in the drawing, is. the flange 16 or 116 is moved away from the lefthand end face of the cylinder block l. The fluid pressure acting against shoulders 14-, 14' on bushing l5 or against shoulders 114, 114 on the boss of bolt 1438 then counteracts and equals the pressure of resilient means 17 or 117. When the pressure in chambers 9, 9 or 199, 10% drops, i.e. when the pump assembly P or P is idling or when the pump is either at a standstill or in the process of being set in operation, the force of spring 17 or 1-17 overcomes the fluid pressure in the chambers and the flange 16 or 116 moves into abutment with the cylinder block 1 upon corresponding axial dis placement toward right of the bushing with respect to block 1 (FIG. 1) or of the bolt 108 with respect to the cylinder block (FIG. 2). In this manner, the righthand end face 7 of the cylinder block is pressed against the control surface '6 or 165 of member 6', hi6, respective-1y. It will thus be seen that, even if no, or only low, pressure prevails in chambers 9, 9 or 1&9, 109, the requisite positioning of end face 7 with respect to the control surface 6 or 166 is insured at all times.

An important advantage of the just-described pumping devices P, -P is in that, due to the provision of twin pressure chambers 9, 9' or 199, 109, requisite positioning of end face 7 on the cylinder block with respect to the control surface 6 or 166 and to the kidney-shaped recesses therein is insured at all times independently of Whether the one or the other of channels 14), 11 or H0, 111 contains fluid at higher or lower pressure. Such purely hydraulic retention of end face 7 with respect to the control surface is insured regardless of whether the diflerence between the pressures prevailing in channels 16, 11 or 119, 111 varies within a wide range, i.e., regardless of the variation in differences between the pressures prevailing at the highand low-pressure sides of the axial piston pump or motor assembly in which the novel system of twin pressure chambers is installed.

While the invention has been shown as embodied in an axial piston pump, it will be readily understood that it may be used with equal advantage and Without substantial modifications in axial piston motor assemblies as well.

Without further analysis the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic and specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. In a structure of the character described, in combination, a rotary cylinder block having a central bore, a pair of spaced annular shoulders in said bore, and two end faces at the opposing ends thereof; a stationary part having a control surface adjacent to the first end face of said block, and a pair of fluid filled recesses formed in said control surface one of which is connected to the highand the other to the lowpressure side of said assembly; a bolt connected to said stationary part and extending into said bore; means carried by said bolt and having a pair of shoulders each slightly spaced from and defining an annular pressure chamber with one of said first mentioned shoulders, said bolt and said stationary part being formed with channels for communicatively connecting each pressure chamber with one of said recesses whereby the chambers are filled with fluid at a pressure prevailing in the respective recess; a flange non-rotatably connected to said bolt and adjacent to the second end face of said block; and resilient means operatively connected with said bolt for constantly urging the flange into abutment with the second end face of said block whereby the latters first end face is urged against said control surface, the fluid pressure in said chambers acting upon each of the first mentioned shoulders to urge the first end face of said block toward said control surface and to move said flange away from the second end face of said block against the action of said resilient means.

2. In an axial piston pump or motor assembly, the combination of a rotary cylinder block having a central bore, a pair of stepped annular shoulders in said bore, and two end faces at the opposing ends thereof; a sta- 6 tionary part having a control surface adjacent to the first end face of said block, and a pair of fluid-filled recesses formed in said control surface one of which is connected to the highand the other to the low-pressure side of said assembly; a bolt connected to said stationary part and extending into said bore; a boss integral with said bolt and having a pair of shoulders each slightly spaced from and defining an annular pressure chamber with one of said first mentioned shoulders, said bolt and said stationary part being formed with channels for communicatively connecting each pressure chamber with one of said recesses whereby the chambers are filled with fluid at a pressure prevailing in the respective recess; a fian e non-rotatably connected to said bolt and adjacent to the second end face of said block; and resilient means operatively connected with said bolt for constantly urging the flange into abutment with the second end face of said block whereby the latters first end face is urged against said control surface, the fluid pressure in said chambers acting upon each of the first mentioned shoulders to urge the first end face of said block toward said control surface and to urge said flange away from the second end face of said block against the action of said resilient means.

3. In an axial piston pump or motor assembly, the combination of a rotary cylinder block having a central bore, a pair of stepped annular shoulders in said bore, and two end faces at the opposing ends thereof; a stationary part having a control surface adjacent to the first end face of said block, and a pair of fluid-filled recesses formed in said control surface one of which is connected to the highand the other to the low-pressure side of said assembly; a bolt integral with said stationary part and extending into and through said bore; a bushing nonrotatably connected with said bolt and axially slidable with respect thereto, said bushing having a pair of shoulders each slightly spaced from and defining an annular pressure chamber with one of said first mentioned shoulders, said bolt and said stationary part being formed with channels for communicatively connecting each pressure chamber with one of said recesses whereby the chambers are filled with fluid at a pressure prevailing in the respective recess, said bushing having a flange adjacent to the second end face of said block; a stop connected to the bolt and adjacent to said flange; and resilient means mounted between said stop and said flange for constantly urging the latter into abutment with the second end face of said block whereby the latters first end face is urged against said control surface, the fluid pressure in said chambers acting upon each of the first mentioned shoulders to urge the first end face of said block toward said control surface and to urge the flange away from the second end face of said block against the action of said resilient means.

4. In an axial piston pump or motor assembly, the combination of a rotary cylinder block having a central bore, a pair of stepped annular shoulders in said bore, and two end faces at the opposing ends thereof; a stationary part having a control surface adjacent to the first end face of said block, a pair of fluid-filled recesses formed in said control surface one of which is connected to the highand the other to the low-pressure side of said assembly, and a bore aligned with the bore of said block; a bolt extending into the bore of said block and into and through the bore of said stationary part, the bolt having a boss formed with a pair of shoulders each slightly spaced from and defining an annular pressure chamber with one of said first mentioned shoulders, said bolt and said stationary part being formed with channels for communicatively connecting each pressure chamber with one of said recesses whereby the chambers are filled with fluid at a pressure prevailing in the respective recess, and said boss having a flange adjacent to the second end face of said block; a stop connected to said bolt externally adjacent to said stationary part; and resilient means mounted between said stop and said stationary part for constantly urging the flange into abutment with the second end face of said block whereby the latters first end face is urged against said control surface, the fluid pressure in said chambers acting upon each of the first mentioned shoulders to urge the first end face of said block toward said control surface and to urge said flange away from the second end face of said block against the action of said resilient means.

In an axial piston pump or motor assembly the combination of a rotary cylinder block having a central bore, a pair of stepped annular shoulders in said bore, and two end faces at the opposing ends thereof; a stationary part having a control surface adjacent to the first end face of said block which is turned away from said shoulders, and a pair of fluid-filled substantially kidneyshaped recesses formed in said control surface one of which is connected to the highand the other to the lowpressure side of said assembly; a bolt connected to said stationary part and extending into said bore; means connected with said bolt and having a pair of shoulders each slightly spaced from and defining an annular recess with one of said first mentioned shoulders, said bolt and said stationary part being formed with channels for communicatively connecting each pressure chamber with one of said recesses whereby the chambers are filled with fluid at a pressure prevailing in the respective recess; a flange non-rotatably connected to said bolt and adjacent to the second end face of said block; and resilient means operatively connected with said bolt for constantly urging the flange into abutment with the second end face of said block whereby the latters first end face is urged against said control surface, the fluid pressure in said chambers acting upon each of the first mentioned shoulders to urge the first end face of said block toward said control surface and to move said flange away from the second end face of said block against the action of said resilient means.

6. In an axial piston pump or motor assembly, the combination of a rotary cylinder block having a central bore, a pair of stepped annular shoulders in said bore, and two end faces at the opposing ends thereof; a stationary part having a control surface adjacent to the first end face of said block, and a pair of fluid-filled recesses formed in said control surface one of which is connected to the highand the other to the low-pressure side of said assembly; a bolt connected to said stationary part and extending into said bore; means connected with said bolt and having a pair of shoulders each slightly spaced from and defining an annular pressure chamber one of said first mentioned shoulders, said bolt and said stationary part being formed with channels for communicatively connecting each pressure chamber with one of said recesses whereby the chambers are filled with fluid at a pressure prevailing in the respective recess; a flange nonrotatably connected to said bolt and adjacent to the second end face of said block; and a plate spring operatively connected with said bolt for constantly urging the flange into abutment with the second end face of said block whereby the latters first end face is urged against said control surface, the fluid pressure in said chambers acting upon each of the first mentioned shoulders to urge the first end face of said block toward said control surface :and to move said flange away from the second end face of said block against the action of said plate spring.

7. In an axial piston pump or motor assembly, the combination of a rotary cylinder block having a central bore, va pair of stepped annular shoulders in said bore, two end faces at the opposing ends thereof, and formed with a plurality of axially parallel cylinder spaces; a plunger reciprocably received in each cylinder space; a rotary wobble plate having an axis incline-d with respect to the axis of said block; and means articulately connected with said wobble plate and with said plungers for reciprocating the letter when said wobble plate rotates, said block being formed with passages extending between said cylinder spa es and the first end face thereof; a stationary part having a control surface adjacent to the first end face of said block, and a pair of fluid-filled recesses formed in said control surface one of which is connected to the highand the other to the low-pressure side of said assembly; a bolt connected to said stationary part and extending into said bore; means connected with said bolt and having a pair of shoulders each slightly spaced from and defining an annular pressure chamber with one of said first imentioned shoulders, said bolt and said stationary part being formed with channels for communicatively connecting each pressure chamber with one of said recesses whereby the chambers are filled with fluid at a pressure prevailing in the respective recess; a flange non-rotatably connected to said bolt and adjacent to the second end face of said block; and resilient means operatively connected with said bolt for constantly urging the flange into abutment with the second end face of said block whereby the latters first end face is urged against said control surface, the fluid pressure in said chambers acting upon each of the first mentioned shoulders to urge the first end face of said block toward said control surface and to move said flange away from the second end face of said block against the action of said resilient means.

8. In an axial piston pump or motor assembly, the combination of a rotary cylinder block having a central bore, a pair of spaced annular shoulders of equal areas in said bore, and .two end faces at the opposing ends thereof; a stationary part having a control surface adjacent to the first end face of said block, and a pair of fluid-filled recesses formed in said control surface one of which is connected to the highand the other to the lowpressure side of said assembly; a bolt connected to said stationary part and extending into said bore; means con nected with said bolt and having a pair of shoulders each slightly spaced from and defining an annular pressure chamber with one of said first mentioned shoulders, said bolt and said stationary part being formed with channels for communicatively connecting each pressure chamber with one of said recesses whereby the chambers are filled with fluid at a pressure prevailing in the respective recess; a flange non-rotatably connected to said bolt and adjacent to the second end face of said block; and resilient means operatively connected with said bolt for constantly urging the flange into abutment with the second end face of said block whereby the latters first end face is urged against said control surface, the fluid pressure in said chambers acting upon each of the first mentioned shoulders to urge the first end face of said block toward said control surface and to move said flange away from the second end face of said block against the action of said resilient means.

9. In an axial piston pump or motor assembly, in combination: a rotary cylinder block having a central bore, a pair of stepped annular shoulders of equal areas in said bore, two end faces at the opposing sides thereof, and formed with a plurality of axially parallel cylinder spaces; a plunger reciprocably received in each cylinder space; a rotary wobble plate having an axis incline-d with respect to the axis of said block; and means articulately connected with said wobble plate and with said plungers for reciprocating the latter when said wobble plate rotates, said block being formed with passages extending between said cylinder spaces and the first end face thereof; a stationary part having a control surface adjacent to the first end face of said block, and a pair of fluid-filled recesses formed in said control surface one of which is connected to the highand the other to the low-pressure side of said assembly; a pin integrally connected to said stationary part and extending into and through the bore of said block; a bushing non-rotatably connected with said pin, axiaily slidable with respect thereto, and having a pair of shoulders each slightly spaced from and defining an annular pressure chamber with one of said first mentioned shoulders, said pin and said stationary part being formed with channels for communicatively connecting each pressure chamber with one of said recesses whereby the chambers are filled with fluid at a pressure prevailing in the respective recess, said bus-hing having a flange adjacent to the second end face of said block; a stop connected to the pin and adjacent to said flange; and resilient means mounted between said stop and said flange for constantly urging the latter into abutment with the second end face of said block whereby the latters first end face is urged against said control surface, the fluid pressure in said chambers acting upon each of the first mentioned shoulders to urge the first end face of said block toward said control surface and to move the flange away from the second end face of said block against the action of said resilient means.

10. In an axial piston pump or motor assembly, in combination: a rotary cylinder block having a central bore, a pair of stepped annular shoulders of equal areas in said bore, two end faces at the opposing sides thereof, and formed with a plurality of axially parallel cylinder spaces; a plunger reciprocably received in each cylinder space; a rotary wobble plate having an axis inclined with respect to the axis of said block; and means articulately connected with said wobble plate and with said pluugers for reciprocating the latter when said wobble plate rotates, said block being formed with passages extending between said cylinder spaces and the first end face thereof; a stationary part having a control surface adjacent to the first end face of said block, a pair of fluid-filled recesses formed in said control surface one of which is connected to the highand the other to the low-pressure side of said assembly, and a bore aligned with the bore of said block; a pin extending into and through the bores in said blocx and in said stationary part, the pin having a boss formed with a pair of shoulders each slightly spaced from and defining an annular pressure chamber with one of said first mentioned shoulders, said pin and said stationary part being formed with channels for communioatively connecting each pressure chamber with one of said recesses whereby the chambers are filled with fluid at a pressure prevailing in the respective recess, and said boss having a flange adjacent to the second end face of said block; a stop connected to the pin and externally adjacent to said stationary part; and resilient means mounted between said stop and said stationary part for constantly urging the flange into abutment with the second end face of said block whereby the latters first end face is urged against said control surface, the fluid pressure in said chambers acting upon each of the first mentioned shoulders to urge the first end face of said block toward said control surface and to move the flange away from the second end face of said block against the action of said resilient means.

11. In an axial piston pump or motor assembly, the combination of rotary cylinder block means having a central bore, a pair of spaced annular shoulders in said bore, and two end faces at the opposing ends thereof; stationary means having a control surface adjacent to the first end face of said block means, and a pair of fluid-filled recesses formed in said control surface one of wlu'ch is connected to the highand the other to the low-pressure side of said assembly; a bolt connected to said stationary means and extending into said bore; a cylindrical member connected with said bolt and having a pair of shoulders each slightly spaced from and defining an annular pressure chamber with one of said first mentioned shoulders, said bolt and said stationary means being formed with channels for communicatively connecting each pressure chamber with one of said recesses whereby the chambers are filled with fluid at a pressure prevailing in the respective recess; a flange non-rotatably connected to said bolt and adjacent to the second end face of said block means; a stop connected to said bolt externally of said block means and said stationary means; a spring inserted between said stop and one of said means for constantly urging the flange into abutment with the second end face of said block means whereby the latters first end face is urged against said control surface, the fluid pressure in said chambers acting upon each of the first mentioned shoulders to urge the first end face of said block means toward said control surface and to move said flange away from the second end face of said block means against the action of said spring.

12. A hydraulic rotary structure of the character described comprising, in combination, a rotary cylinder block, axially directed displacement cylinder chambers formed in said cylinder block at angular spacings about the axis of rotation of said block, ports formed in a first transverse end face of the cylinder block each communicating with a respective cylinder chamber and located closer to the axis of rotation of said cylinder block than to the axis of said respective cylinder chamber; a nonrotative plate means abutting said end face of said cylinder block, an inlet port and an outlet port in said plate means arranged for cooperation with said ports in the cylinder block for inlet and outlet, respec ively, of hydraulic fluid; a piston reciprocable in each cylinder chamber, 21 wobble plate rotatable conjointly with said cylinder block, said wobble plate disposed in use at an angle to said axis of rotation and operatively connected to said pistons to effect reciprocation during rotation of the cylinder block; a central bore formed in said cylinder block and having a pair of spaced annular shoulders; a bolt connected to said plate means and extending into said bore; means carried by said bolt and having a pair of shoulders each slightly spaced from and defining an annular pressure chamber with one of said first mentioned shoulders and said bore, said pressure chambers being disposed concentrio with the axis of rotation of said cylinder block, said bolt and said plate means having channels for communicatively connecting each pressure chamber with one of said ports in said plate means whereby the pressure chambers are filled with said hydraulic fluid at a pressure prevailing in the repective port; a flange nonrotatively connected to said bolt and adjacent a second transverse end face of said cylinder block, said second transverse end face being disposed opposite said first transverse end face of said block; said flange being axially displaceable with respect to said second transverse end face of said cylinder block; resilient means operatively connected with said bolt for constantly urging the flange into abutment with the second end face of said cylinder block whereby the latters first end face is urged against said valve plate, the fluid pressure in said chambers acting upon each of the first mentioned shoulders to urge the first end face of said block toward said valve plate and upon each of the second mentioned shoulders to move said flange away from the second end face of said cylinder block against the action of said resilient means.

References Qited in the file of this patent UNITED STATES PATENTS 1,137,283 Pratt Apr. 27, 1915 1,163,849 Pratt Dec. 14, 1915 1,817,080 Howard Aug. 4, 1931 2,661,701 Ferris Dec. 8, 1953 2,861,552 Creighton et al Nov. 25, 1958 2,895,426 Orshansky July 21, 1959 2,900,921 Brown Aug. 25, 1959 2,987,006 Bowers et al June 6, 1961 FOREIGN PATENTS 760,783 Germany Apr. 16, 1953 1,003,040 Germany Feb. 21, 1957 

1. IN A STRUCTURE OF THE CHARACTER DESCRIBED, IN COMBINATION, A ROTARY CYLINDER BLOCK HAVING A CENTRAL BORE, A PAIR OF SPACED ANNULAR SHOULDERS IN SAID BORE, AND TWO END FACES AT THE OPPOSING ENDS THEREOF; A STATIONARY PART HAVING A CONTROL SURFACE ADJACENT TO THE FIRST END FACE OF SAID BLOCK, AND A PAIR OF FLUID FILLED RECESSES FORMED IN SAID CONTROL SURFACE ONE OF WHICH IS CONNECTED TO THE HIGH- AND THE OTHER TO THE LOW-PRESSURE SIDE OF SAID ASSEMBLY; A BOLT CONNECTED TO SAID STATIONARY PART AND EXTENDING INTO SAID BORE; MEANS CARRIED BY SAID BOLT AND HAVING A PAIR OF SHOULDERS EACH SLIGHTLY SPACED FROM AND DEFINING AN ANNULAR PRESSURE CHAMBER WITH ONE OF SAID FIRST MENTIONED SHOULDERS, SAID BOLT AND SAID STATIONARY PART BEING FORMED WITH CHANNELS FOR COMMUNICATIVELY CONNECTING EACH PRESSURE CHAMBER WITH ONE OF SAID RECESSES WHEREBY THE CHAMBERS ARE FILLED WITH FLUID AT A PRESSURE PREVAILING IN THE RESPECTIVE RECESS; A FLANGE NON-ROTATABLY CONNECTED TO SAID BOLT AND ADJACENT TO THE SECOND END FACE OF SAID BLOCK; AND RESILIENT MEANS OPERATIVELY CONNECTED WITH SAID BOLT FOR CONSTANTLY URGING THE FLANGE INTO ABUTMENT WITH THE SECOND END FACE OF SAID BLOCK WHEREBY THE LATTER''S FIRST END FACE IS URGED AGAINST SAID CONTROL SURFACE, THE FLUID PRESSURE IN SAID CHAMBERS ACTING UPON EACH OF THE FIRST MENTIONED SHOULDERS TO URGE THE FIRST END FACE OF SAID BLOCK TOWARD SAID CONTROL SURFACE AND TO MOVE SAID FLANGE AWAY FROM THE SECOND END FACE OF SAID BLOCK AGAINST THE ACTION OF SAID RESILIENT MEANS. 